TWI500447B - Composition comprising a multi-layer halogenated polyolefin microporous membrane, a filter comprising it and a method of making the same - Google Patents

Description

Composition comprising multi-layer halogenated polyolefin microporous membrane, filter comprising same and manufacturing method thereof

The present invention relates to a porous membrane treated by atmospheric pressure microwave plasma and a method of producing the same.

Filtration can be used in the pharmaceutical, microelectronics, chemical, and food industries to provide product purity and process purity. In such applications, the porous membrane removes particulate contaminants, ionic contaminants, and other contaminants from the fluid. The pore size of the porous membrane is in the range of ultrafiltration (about 0.001 μm) to microfiltration (about 10 μm), and can be made of a chemically compatible and mechanically stable polymer matrix with measurable retention and pore size. Or pore size distribution and thickness. The pore size in the microporous membrane can range from about 0.01 to about 5.0 microns, and can be selected based on the particle size or type of impurities to be removed in the application, pressure drop requirements, and viscosity requirements. In use, the porous membrane is typically incorporated into a device suitable for insertion into a fluid stream for self-contained process fluid removal of particulates, microorganisms or solutes.

When filtering or purifying the fluid, the process fluid is typically passed through a membrane filter at a pressure differential across the membrane which forms a higher pressure zone on the upstream side of the membrane than on the downstream side. The filtered liquid is subjected to a pressure drop across the porous membrane and the membrane is subjected to mechanical stress. This pressure difference can also cause the dissolved gas to precipitate from the liquid; the liquid on the upstream side of the porous membrane has a higher dissolved gas concentration than the liquid on the downstream side of the porous membrane. This is because the gas (such as air) has a higher solubility in the liquid under high pressure than in the liquid at low pressure. when When the liquid flows from the upstream side to the downstream side of the porous membrane, the dissolved gas escapes from the solution and forms bubbles in the liquid and/or on the surface of the porous membrane. This gas evolution is commonly referred to as degassing of liquids. The degassing of the liquid can also occur spontaneously without pressure difference, as long as the liquid contains dissolved gas and there is a driving force for the gas to escape the solution, such as a nucleating position that causes bubbles or cavitation to form on the surface of the porous membrane (nucleating) Site), temperature change or chemical composition change. Degassing liquids commonly used in the manufacture of pharmaceuticals, semiconductor devices and displays may include very high purity water, ozone water, peroxide containing liquids, organic solvents such as alcohols, and other chemically active liquids such as acids which may contain oxidizing agents or A concentrated aqueous solution of the base).

The use of a chemically inert filter facilitates membrane filtration of such chemically active liquids to prevent membrane degradation and loss of integrity that may result in the release of the extractable material from the filter during use. Membrane filters made from halogenated polyolefins such as fluoropolymers such as polytetrafluoroethylene have been commonly used in such applications. The chemical inertness of fluoropolymers and their excellent resistance to chemical attack are well known. Fluoropolymer films have low surface energy and are hydrophobic. Therefore, films made of such polymers are difficult to wet with aqueous liquids or other liquids (the liquids have a surface tension that is significantly higher than the surface energy of the film. During the filtration of the degassing liquid using a hydrophobic porous membrane, The porous membrane provides a nucleation site for the dissolved gases that escape from the solution under the driving force of the differential pressure during the filtration process. Such nucleation on the surface of the hydrophobic membrane (including internal pore surfaces and external or geometric surfaces) The gas that escapes from the solution at the location forms a cavitation that adheres to the membrane. The cavitation increases in size as it is continuously degassed, so that it may begin to vent the liquid from the pores of the membrane, which reduces the The effective filtration area of the membrane. This phenomenon is commonly referred to as dehumidification of the porous membrane due to the liquid wetting of the porous membrane or the gradual conversion of the liquid-filled portion into a gas-filled portion.

Dewetting of the porous membrane can also occur spontaneously when a wet film, such as a hydrophobic membrane that is wetted with an aqueous fluid, is exposed to a gas, such as air. This dehumidification phenomenon has been found to occur more frequently and more significantly in fluorocarbon based membranes. It has also been found that the rate of dehumidification occurring in small pore size membranes (such as 0.2 microns or less) is higher than in larger pore size membranes.

Therefore, as the membrane filter is dehumidified over time, it becomes more difficult to purify or filter the same volume of process fluid per unit time as compared to when the filter is newly installed and completely wet. Installing a new filter, rewet the dehumidification filter, or changing the process to compensate for liquid flow reduction translates into higher operating costs for the user. Rewetting takes time, usually with flammable liquids that must be treated, and requires time consuming flushing.

The surface of the PTFE membrane has been treated to alter its properties and to make it more hydrophilic. A method described in International Patent Publication No. WO 03/070784 discloses a film by exposing a film to a reactant solution (for example, sodium hydrogen borate and ruthenium in a solvent such as dichloromethane) and the film And a method in which the solution is exposed to heat or ultraviolet light to improve the biocompatibility of the film. International Patent Publication No. WO/04/007060 discloses a method of modifying a PTFE membrane via ultraviolet radiation in the presence of Na ₂ SO ₃ or other chemicals. These methods involve the use of sodium-containing reagents which can result in metal extractables from the membrane and require extensive rinsing of the membrane prior to use in high purity applications. Another method for producing a hydrophilic PTFE film is to coat PTFE with a hydrophilic chemical as described in U.S. Patent Application Publication No. 20020144944 and International Patent Publication No. WO/01/58577. The coated porous film can be used to modify the surface energy of the composite film, however the coating is typically applied to the film from a solvent (e.g., an organic solvent) and requires a curing step. This coating method changes the pore size of the porous membrane and forms chemical waste that needs to be removed and treated, thereby increasing the cost and time of film manufacture.

The porous PTFE membrane can be modified using a drying method. U.S. Patent No. 5,282,965 discloses the treatment of PTFE membranes by radio frequency (RF) vacuum plasma at a pressure of between about 0.01 Torr and 10 Torr to effect membrane modification and to prevent membrane fibril destruction. It is also disclosed that the film is placed at an electrode to film distance of 1 to 20 cm to prevent or avoid damage to the film surface. It is not apparent from this disclosure that atmospheric pressure or contact of the porous membrane with the electrode can be used to modify the membrane without causing fibril destruction or membrane damage (which can result in weakening of the porous membrane).

US 6,074,534 discloses a device for carrying out a method of increasing the wettability of a porous body in a microwave-generated plasma under vacuum conditions. These porous systems are made of sintered powder (example Made of polyethylene) to form a marking tip having pores in the range of from 1 micron to about 50 microns. This disclosure does not disclose a composition or how to treat a porous film or a relatively microporous film of a relatively inert polymer (e.g., PTFE) under atmospheric pressure to form a porous material having stable wettability and high strength.

Microwave-coupled atmospheric pressure unbalanced plasma is used (Shenton et al. J. Polymer Science: Part A, Vol. 40, 95-109, (2002) and Shenton et al. J. Phys D: Applied Physics, Vol. 34, 2761- 2768, (2001)), Shenton observed surface cleaning of non-porous general polymer matrices (such as HDPE, LDPE, polypropylene, and PET) from 0.1 to 1 mm thick (removing such as grease, release agents, or surface contaminants) Boundary layer), cross-linking and branching, and surface chemical structure modification. Shenton observed an increase in surface properties such as the surface energy of the substrate. Shenton et al. did not modify the porous film and did not prepare a porous film with long-term wettability that was non-dehumidified and substantially retained the strength of the base film to contact the wetted material.

U.S. Patent No. 6,709,718 discloses RF atmospheric plasma treatment of a porous membrane comprising a cavitating agent. The RF atmospheric plasma treatment is said to improve the hydrophilic nature of the membrane, including polyolefin porous sheets of 0.1 to 10 micron pores of the cavitating agent. The film sample subjected to the ink penetration test has a value of less than about 60%, indicating that the porous film is not completely wettable by contact with the ink.

U.S. Patent No. 5,895,558 discloses the treatment of atmospheric pressure RF plasma (13.5 MHz) of plastic film, web or porous substrate to render it hydrophilic. Short processing times (e.g., 15, 8 and 5 seconds) were applied to the spunbonded polypropylene sample to make it water wet. The materials are not immediately wettable and are shown to require an absorption time of from about 3 to about 10 seconds. Short exposure times and thick meltblown materials are used to reduce damage to the treated substrate. It is not obvious to use a longer treatment time to form a hydrophilic material, especially on a thin porous membrane, without causing loss to the membrane.

U.S. Patent No. 6,118,218 discloses the incorporation of a porous metal layer in one of the electrodes of a plasma processing system. Plasma gas is injected into the electrode at substantially atmospheric pressure and allowed to diffuse through the porous layer, thereby forming a uniform glow discharge plasma. In plasma under atmospheric conditions Treatment of organic films commonly used in the food packaging industry (such as polypropylene, polyethylene, and polyethylene terephthalate substrates). There are no significant differences in the results using multiple AC voltage frequencies in the 60 Hz to 20 kHz range. It has been disclosed that a stable glow discharge can be produced at frequencies well below the previously possible frequencies. Many routine tests were successfully performed at 1 kHz and produced good glow discharges at frequencies as low as 60 Hz. The surface energy of the modified film is shown to decrease over time after atmospheric plasma treatment, with some reductions of up to 20% or more.

T. Kasemura, S. Ozawa, K. Hattori, "Surface Modification of Fluorinated Polymers by Microwave Plasmas," J. Adhesion, 33: 33 (1990). Improvements in film samples treated by microwave plasma under decreasing pressure are observed. Wet.

Forms of the invention include compositions comprising a porous polymeric film wherein one or more surfaces of the film have been modified by atmospheric pressure microwave (APMW) plasma. The plasma modified membrane is non-dehumidified and can be wetted upon contact with the first aqueous solution of MeOH, wherein the minimum amount of MeOH first aqueous solution used to contact the porous membrane modified to wet the APMW plasma is less than The minimum amount of MeOH reference aqueous solution or control aqueous solution used to contact the untreated pure sample that wets the porous membrane. In some versions of the invention, the film is modified when in contact with the rotating electrode of the plasma generating device. The film can be used in a variety of materials (including filters and liquid films) for heat and mass transfer.

Certain versions of the invention are compositions comprising an uncoated porous polymeric film made from a halogenated polyolefin, wherein one or more surfaces of the film have a structure and chemistry modified by atmospheric pressure microwave plasma treatment nature. The plasma modified membrane was non-dehumidified and wetted with 96% by weight or less of MeOH aqueous solution (while the untreated sample was contact wetted with 97% by weight aqueous MeOH solution).

The surface of the film can be modified in an AMPW plasma containing an oxygen source. The membrane modified by the non-dewetting surface may have a different oxygen/carbon ratio than the untreated membrane. Type of porous membrane composition Wherein the O/C ratio characterizes a film that is uniformly wettable with a first aqueous solution of MeOH, wherein the minimum amount of MeOH in the first aqueous solution used to contact the porous membrane modified by the APMW plasma is compared to The minimum amount of MeOH in the reference aqueous solution or control aqueous solution that contacts the untreated pure sample that wets the porous membrane is at least 1% by weight less. In some versions, the first solution is a mixture of methanol and water having 96% by weight or less of MeOH. In some versions of the invention, the O/C ratio of the surface of the modified membrane may be between about 0.06 and about 0.08. In some versions of the invention, the O/C ratio of the surface of the modified membrane may be between about 0.04 and about 0.08.

The surface of the porous membrane modified by atmospheric pressure microwave plasma in the form of the present invention has a surface functional group and morphology which allows it to be wetted by contact with the first aqueous solution of MeOH, wherein the first surface for contacting and wetting the porous membrane The minimum amount of MeOH in the aqueous solution is at least 1% by weight less than the minimum amount of MeOH in the reference aqueous solution used to contact the untreated pure sample that wets the porous membrane, and in some versions is at least 4% by weight less. . The contact wettability of the surface of the microwave plasma treated polymeric film remains constant or substantially constant over a period of 10 days or more and/or remains stable or substantially stable. The plasma-modified polymer porous membrane is non-dehumidified so that the composition is always wetted by the liquid after contact with the gas-containing liquid.

The porous membrane modified by atmospheric pressure microwave plasma may be a single layer having a pore or pore distribution that provides retention of the sieved particles. In some versions, the porous membrane can comprise one or more layers, which can have pores of the same or different sizes in each layer. The porous membrane can have a thickness and chemical resistance suitable for its intended use, and in some versions the film has a thickness of less than about 30 microns. The porous membrane can be uncoated.

In the version of the invention, the combination of microwave power, film temperature, gas type and gas flow rate, plasma density and processing time functionalizes the surface of the porous membrane and provides improved and stable wettability while remaining substantially unchanged. The strength of the porous membrane. The combination of plasma conditions provides a non-dehumidified porous membrane. The porous membrane modified by atmospheric pressure microwave plasma surface The strength may be at least 70%, at least 80% or at least 90% or more of the strength of the porous membrane of the surface modified microwave plasma without atmospheric pressure.

One version of the invention is a composition comprising a microporous polymeric membrane of a halogenated polyolefin having a sieved LRV of at least 3 for particles of 0.1 micron or less in a liquid such as water. The microporous membrane has one or more surfaces modified by atmospheric pressure microwave plasma on the membrane, and the surfaces are fast (for example, 1 to 2) with 96% by weight or less of MeOH aqueous solution placed on the modified surface. Seconds) and evenly wetted. The surface of the porous membrane modified by the APMW plasma is stable such that the wettability of the composition is unchanged or substantially after 10 days or more (in some versions, stored in the surrounding environment for 70 days or more). Same on the same. The porous membrane of the type of the present invention may include a surface modified by atmospheric pressure microwave plasma (containing a rare gas or a rare gas having an oxygen source). The atmospheric pressure microwave plasma modified porous membrane has a sieved LRV of at least 3 for particles of 0.1 micron or less in a liquid such as water. In some versions, the microporous polymer film is uncoated prior to atmospheric pressure microwave plasma treatment.

One version of the invention is a composition comprising or comprising a microporous polymeric membrane of a halogenated polyolefin having a sieved LRV of at least 3 for particles of 0.1 micron or less in a liquid such as water. The microporous membrane has one or more atmospheric pressure microwave plasma modified surfaces wetted by solution contact on the membrane, wherein a minimum amount of methanol in the aqueous solution for contacting the wetted porous membrane is contacted. The minimum amount of methanol in the reference aqueous solution used to contact the wetted untreated porous membrane is at least 1% by weight, and in some versions at least 4% by weight. The surface of the APMW plasma-modified porous membrane is stable such that the composition is wet after 10 days or more (in some versions, stored in air as a dry film in the surrounding environment for 70 days or more) The sex is unchanged or substantially the same. The porous membrane of the type of the invention may comprise a surface modified by atmospheric pressure microwave plasma (containing a rare gas or a rare gas having an oxygen source). The atmospheric pressure microwave plasma modified porous membrane has a sieved LRV of at least 3 for particles of 0.1 micron or less in a liquid such as water. In some versions, the micro The pore polymer film was uncoated prior to atmospheric pressure microwave plasma treatment.

The surface of the microporous membrane can be modified in a plasma that may contain an oxygen source. The membrane modified by the non-dewetting surface may have a different oxygen/carbon ratio than the base microporous membrane not treated by the plasma. In the form of the composition, the O/C ratio of the modified surface characterizes a film that is uniformly wetted or contacted with a first aqueous solution of MeOH, wherein the MeOH in the first aqueous solution that wets the porous membrane is contacted. The minimum amount is at least 1% by weight less than the minimum amount of MeOH in the reference aqueous solution used to contact the untreated sample that wets the porous membrane. In some versions of the invention, the O/C ratio of the surface of the modified microporous membrane can be between about 0.04 and about 0.08 or from about 0.06 to about 0.08. In some versions, the microporous polymer film is uncoated prior to atmospheric pressure microwave plasma treatment using a plasma comprising an oxygen source.

The atmospheric pressure microwave plasma modified surface of the polymeric microporous membrane has a surface functional group and a structure or morphology wetted with a first aqueous solution of MeOH, wherein the MeOH in the first aqueous solution that wets the porous membrane is contacted The minimum amount is at least 1% by weight less than the minimum amount of MeOH in the reference aqueous solution used to contact the untreated sample that wets the porous membrane, wherein the wettability of the surfaces is substantially after 10 days or more Constant or substantially stable. The surface of the polymer-modified polymer porous membrane is non-dehumidified so that the composition is always wetted by the liquid after contact with the gas-containing liquid.

The microporous membrane modified by atmospheric pressure microwave plasma can be a single layer having a pore or pore distribution that provides retention of the sieved particles. In some versions, the microporous membrane can comprise one or more layers, which can have pores of the same or different sizes in each layer. The microporous film can have a thickness and chemical resistance suitable for its intended use, and in some versions the film thickness is less than about 30 microns. In some versions of the invention, the microporous membrane modified by atmospheric pressure microwave plasma may have a sieved LRV of at least 3 for particles of 0.1 micron or less in the liquid; in some versions, for liquids The particles of 0.05 microns or less may have a sieved LRV of at least 3, and in other versions, may have a sieved LRV of at least 3 for particles of 0.03 microns or less in the liquid.

The conditions of power, temperature, gas type and gas flow rate, plasma density and plasma treatment time functionalize the surface of the porous membrane and form a contactable wetted porous membrane which is non-dehumidified after contact with the gas containing liquid And it generally maintains the strength properties of the untreated film. The strength of the porous membrane surface modified by atmospheric pressure microwave plasma is at least 70%, at least 80% or at least 90% of the strength of the porous membrane having no atmospheric pressure microwave plasma modified surface. These microporous membranes modified by atmospheric plasma can be used in a variety of applications, including filters and liquid membranes.

One form of the invention is a method of altering the lyophilicity of one or more surfaces of a porous article. The method can include the act of contacting a porous membrane (in some cases an uncoated porous membrane) with a gas containing atmospheric pressure microwave plasma and treating the surface of one of the porous membranes using the plasma. The treated porous membrane surface can include nodes, fibrils, pore interiors, pore portions, membrane outer surfaces, and combinations of the foregoing. The surface of the porous membrane interacts with and/or reacts with the plasma. The interaction of the plasma with the porous membrane continues until the contact wettability of the article is increased such that the porous membrane is non-wetting and the strength or average strength of the membrane does not fall below about 70% of the strength of the uncoated porous membrane. This process can be carried out in a continuous process.

In some versions of the invention the porous membrane is a microporous membrane, and in other versions the porous membrane can be an uncoated microporous membrane. The microporous membrane may have a sieved LRV of at least 3 for particles of 0.1 micron or less in the liquid; at least 3 sieved LRV for particles of 0.05 micron or less in the liquid; 0.03 micron or more for the liquid The small particles may have a sieved LRV of at least 3. The porous or microporous membrane may comprise a halogenated polyolefin.

Embodiments of the invention may include a composition comprising a halogenated polyolefin microporous membrane, wherein the microporous membrane has a sieved LRV of at least 3 for particles of 0.1 micron or less in the liquid, the modified membrane having a Or a plurality of surfaces having an O/C ratio greater than about 0.06. The embodiment of the porous membrane may be wetted by contact with 96% by weight or less of MeOH aqueous solution after 10 days or more, and non-dehumidified after autoclaving treatment in water at a temperature of about 135 ° C for about 40 minutes. In some versions of the composition, the halogenated polyolefin is polytetrafluoroethylene. combination The pattern may be a microporous film having a web direction (WD) strength and a machine direction (MD) strength of at least 12 Newtons when the film has a thickness of about 30 microns or less. In certain embodiments, the porous membrane may be wetted by contact with 94% by weight or less of MeOH aqueous solution and non-dehumidified after autoclaving at about 135 ° C for about 40 minutes.

The contactable wettable microporous membranes can have one or more regions or layers and in total have less than about 200 ppb of extractable ions (including calcium ions and sodium ions). In certain embodiments, the O/C ratio of the surface of the porous membrane is in the range of from about 0.06 to about 0.08.

The surface of the porous membrane can be modified in an atmospheric microwave plasma that can include an oxygen source (and in some versions an inert gas that is different from air or a source of oxygen in a rare gas). The porous membrane modified by the non-dewetting surface may have a different oxygen/carbon ratio than the non-plasma treated base porous membrane. In the form of the composition, the O/C ratio of the modified surface characterizes a porous membrane that can be uniformly wetted or contacted with a MeOH aqueous solution, wherein the minimum amount of MeOH in the aqueous solution to contact the wetted porous membrane is contacted. The minimum amount of MeOH in the reference aqueous solution used to contact the untreated sample that wets the porous membrane is at least 1% by weight less. In some versions of the invention, the O/C ratio of the surface of the modified porous membrane can be between about 0.04 and about 0.08 or from about 0.06 to about 0.08.

Atmospheric pressure microwave plasma processes form a modified surface on a polymeric porous membrane having surface functional groups and a structure or morphology that can be wetted (and preferably contact wetted) with aqueous MeOH, wherein the contact is wetted The minimum amount of MeOH in the aqueous solution of the porous membrane is at least 1% by weight less than the minimum amount of MeOH in the reference aqueous solution used to contact the untreated sample that wets the porous membrane, and wherein the wettability of the surfaces It is substantially constant or substantially stable after 10 days or more. The surface of the polymer porous membrane modified by atmospheric pressure microwave plasma is not dehumidified so that the composition is always wetted by the liquid after contact with the gas containing liquid.

This method can be used to modify uncoated or coated porous membranes. In some versions of the invention, the porous membranes can be microporous membranes. Atmospheric pressure microwave in the form of the invention The plasma process can be used to modify a porous membrane that can include one or more layers. For example, the porous membrane can have a single layer having a pore or pore distribution that provides for the retention of the sieved particles. In some versions, the porous membrane can comprise one or more layers, which can have pores of the same or different sizes in each layer. The microporous film can have a thickness and chemical resistance suitable for its intended use, and in some versions the film thickness is less than about 30 microns. The atmospheric pressure microwave plasma method can be used to modify a microporous membrane such that it has a sieved LRV of at least 3 for particles of 0.1 micron or less in a liquid such as deionized water or pure water; The micron or smaller particles have a sieved LRV of at least 3; and have a sieved LRV of at least 3 for particles of 0.03 micron or less in the liquid.

Power, temperature, gas type and gas flow rate, plasma density and atmospheric pressure The conditions of the microwave plasma treatment method make the surface of the porous membrane functional; the porous membrane formed by the method is contact wettable, non-dehumidified And maintain most or most of the strength of the untreated film. The strength of the porous membrane surface modified by atmospheric pressure microwave plasma is at least 70% of the strength of the porous membrane of the microwave plasma modified surface without atmospheric pressure, at least 80% in some versions or at least 90 in other types. %. The film was non-dehumidified after autoclaving in water at a temperature of about 135 ° C for 40 minutes or about 40 minutes. These atmospheric membrane-modified porous membranes can be used in a variety of articles, including filters and liquid membranes.

The method for treating a porous membrane with atmospheric pressure microwave plasma may include an atmosphere comprising a gas that improves the contact wettability of the membrane. In certain embodiments, the gas can include a source of oxygen. In some versions, the source of oxygen may be present in the mixture with an inert gas, a noble gas (such as helium), or a combination thereof, wherein the composition of the plasma gas is different from air. The oxygen source can be any oxygenate. In certain embodiments, the source of oxygen can be a compound such as water vapor, alcohol, oxygen, or a combination of the foregoing. In some versions, the source of oxygen is air. The type of the invention comprises an APMW treatment with the gases to form a porous membrane of a modified porous membrane, as measured by a solution of different MeOH and water, compared to the untreated membrane sample. Improved contact wettability; in some versions, The APMW plasma treated membrane may be wetted by contact with an aqueous solution of MeOH, wherein the minimum amount of MeOH in the aqueous solution used to contact the wetted porous membrane is compared to the reference aqueous solution used to contact the untreated sample that wets the porous membrane. The minimum amount of MeOH is at least 1% by weight, and in some embodiments at least 4% by weight.

The method can further comprise combining the atmospheric pressure microwave plasma modified porous membrane with one or more supports such as, but not limited to, webs, screens, filter cartridges, filter cages, end caps, or any combination thereof. The act or step of forming a variety of items, such as filters. The film may be further modified by pleating the modified film with one or more optional supports such as, but not limited to, screens, webs, drainage layers, or combinations of such.

The type of the invention advantageously provides a surface modified porous membrane having improved wettability and improved non-dehumidifying properties compared to an untreated base film without fibrils or other particulate screening structures. loss. The porous membrane material modified by atmospheric plasma microwave retains the large half strength and particle retention properties of the base membrane. This treatment unexpectedly results in improved and stable wettability throughout the thickness of the porous film under atmospheric pressure.

Advantageously, the porous membrane modified by atmospheric pressure plasma in the form of the invention may be uncoated. For example, atmospheric pressure microwave plasma treatment can form a non-dehumidified porous membrane without the use of a perfluorocarbon copolymer component or other adhesive coating to render the membrane surface non-dehumidifying and contact wettable.

Atmospheric pressure microwave plasma treatment of the membranes of the present invention can be used in a continuous process to produce a lyophilic wettable membrane having substantially the same strength as an untreated porous membrane. Since the process can be carried out under atmospheric pressure, a vacuum pump is not used, which reduces the process time and operating cost compared to the vacuum plasma treatment of the porous membrane. Since the solution-based coating applied externally on the porous membrane is not used to directly wet the porous membrane, the potential for flow loss and/or additional extractables can be minimized or avoided. Similarly, since the organic liquid and the ion-containing reagent are not used to modify the surface of the porous membrane in the type of the present invention, the porous membrane and the method for producing the same can avoid such as sodium ion and other metal separation. Sub-contaminants, as well as a large number of rinses, drying and treatment of membrane modification solvents or reagents.

Before the present compositions and methods are described, it is to be understood that the invention is not limited to the particular sings, compositions, methods or procedures described, as such may vary. It is also to be understood that the terms used in the description are only for the purpose of describing the particular embodiments, and are not intended to limit the scope of the invention, which is limited by the scope of the appended claims.

It must also be noted that the singular forms "a" and "the" Thus, for example, reference to a "pore" refers to one or more apertures and equivalents known to those skilled in the art, and the like. Unless otherwise defined, all technical and scientific terms used herein have the same meaning meaning Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the forms of the present invention, non-limiting examples of methods, devices, and materials are now described. All publications mentioned herein are incorporated by reference. Nothing herein is to be construed as an admission that the invention is

The version of the invention comprises a porous polymeric membrane wherein one or more surfaces of the membrane have been modified by atmospheric pressure microwave (APMW) plasma. The film can be made from a halogenated polyolefin such as, but not limited to, polytetrafluoroethylene or modified polytetrafluoroethylene. The porous polymeric membrane can be an uncoated porous membrane and in some versions is a microporous membrane.

In some versions, the porous polymeric membrane of the present invention, i.e., the surface modified by atmospheric pressure microwave (APMW) plasma, has an oxygen/carbon ratio different from that of the untreated membrane, and in certain embodiments. There is a porous membrane surface O/C ratio between 0.06 and 0.08. The porous membrane modified by atmospheric pressure microwave (APMW) plasma has a surface structure such that the minimum amount of methanol in the aqueous solution used to contact the wetted porous membrane is compared to that used for contact wetting (non-APMW) Plasma treatment) The minimum amount of methanol in the reference aqueous solution of the untreated sample of the porous membrane is at least 1% by weight; in some versions, the contact is used to wet the treatment. The minimum amount of methanol in the aqueous solution of the apertured membrane is at least 4% by weight less than the minimum amount of methanol in the reference aqueous solution used to contact the wetted untreated porous membrane. In some versions of the invention, the APMW plasma treated porous membrane is non-dehumidified after autoclaving for 40 minutes in water at a temperature of 135 °C.

The type of porous membrane modified by atmospheric pressure microwave (APMW) plasma surface may have a surface structure such that the treated membrane may be wetted by a first solution of methanol and water mixture having 96% by weight or less of methanol. In some versions, the treated porous membrane can be wetted by contact with a 96% by weight aqueous methanol solution after 10 days. The porous membrane can be a perfluorinated material, a halogenated polyolefin or other composition.

The porous polymer membrane treated by atmospheric pressure microwave plasma can be a single layer membrane having a pore size or pore size distribution that provides retention of the sieved particles. In some versions, the treated porous membrane comprises a plurality of layers having pores of the same size in each layer, or in other versions, the porous membrane can comprise a plurality of layers having pores of different sizes in each layer . The APMW treated microporous membrane has a sieved LRV of at least 3 for particles of 0.1 micron or less in water. The APMW plasma treated microporous membrane having one or more regions or layers may have a total of less than 200 ppb of extractable ions (e.g., overnight extraction by 10% HCl), including calcium ions and sodium ions.

In certain versions of the invention, the APMW plasma treated microporous membrane having one or more regions or layers may have a strength of at least 70% of the strength of the untreated porous membrane, and in some versions The thickness of the microporous membrane can be less than 30 microns. In some versions, the APMW plasma treated microporous membrane having one or more regions or layers can have a web orientation (WD) strength and processing of at least 12 Newtons when having a thickness of about 30 microns or less. Direction (MD) intensity.

One form of the invention is a method of treating a porous article (e.g., a porous membrane or a microporous membrane) to modify the lyophilicity of one or more surfaces thereof, the method comprising subjecting the porous article to atmospheric pressure microwave plasma containing a gas Step of contacting and treating the surface of one of the porous articles with the plasma Step. The porous membrane can be a coated or uncoated porous membrane.

The strength of the porous polymeric film (also including the microporous film) treated by this method can be at least 70% of the strength of the untreated porous film. In some versions, the APMW plasma treated microporous membrane having one or more regions or layers may have a web orientation (WD) strength and processing direction of at least 12 Newtons when having a thickness of 30 microns or less. (MD) strength.

The porous or microporous membrane may comprise a halogenated polyolefin. In some versions, the film can include polytetrafluoroethylene or modified polytetrafluoroethylene. In some versions, the microporous polymer film can be uncoated prior to atmospheric pressure microwave plasma treatment.

Atmospheric pressure microwave plasma treatment methods can be used to treat porous membrane surfaces selected from the group consisting of: nodes, fibrils, pore interiors, pore fractions, membrane exterior surfaces, and any combination of these to make them untreated The surface of the porous membrane is more hydrophilic or lyophilic. This treatment is used to alter the dehumidification properties of the porous article. In some versions of the invention, the interaction of the plasma with the porous membrane continues until the contact wettability of the treated membrane is increased such that the treated porous membrane is non-wetting and the strength or average strength of the membrane does not decrease. Up to 70% of the strength of the untreated porous film.

In some versions of the method, the surface of the membrane is modified in an APMW plasma comprising an oxygen source. The source of oxygen can be selected from the group consisting of water vapor, alcohol, air, or any combination of the foregoing. In some versions of the method the plasma contains a rare gas, and in other versions it contains only one or more noble gases or inert gases. The APMW plasma treatment of the film can be carried out from a reel of porous material sheets in a continuous process.

The APMW plasma treated porous membrane can be bonded to one or more supports. The supports can be selected from the group consisting of webs, screens, filter cartridges, filter cages, end caps, or any combination thereof to form a filter cartridge. In some versions of the invention, the treated film can be further modified by pleating the modified film with one or more supports. The support for the pleated membrane may be selected from the group consisting of a mesh, a web, a drainage layer, or any combination thereof.

The type of the invention may include a polymer porous membrane composition and a side for producing the same The polymeric porous membrane composition comprises one or more surfaces modified by atmospheric pressure microwave plasma on the membrane. Atmospheric pressure microwave plasma treatment of the porous membrane provides contact with the wetted material with an aqueous MeOH solution, wherein the minimum amount of MeOH in the aqueous solution used to contact the wetted porous membrane is less than the untreated sample used to contact the wetted porous membrane The minimum amount of MeOH in the control aqueous solution. The compositions may also provide stable wettability, retain most of the mechanical strength of the base film, have a low level of extractables, be a non-dehumidified porous film, or a combination of such properties.

The porous membranes may be prepared by a process which may include the act or step of contacting one or more surfaces of the porous polymeric membrane with a microwave generating plasma having a gas at about atmospheric pressure until the porous membrane Methanol can be wetted by contact with a solution of water containing less methanol than the methanol and aqueous solution used to contact the wetted untreated porous membrane. In some versions the method forms a wetted modified halogenated polyolefin porous membrane that can be contacted with a 96% by weight or less aqueous methanol solution, and in some versions the modified porous membrane can be used with 95% by weight or less of MeOH aqueous solution. Contact wetting; in some versions the modified porous membrane may be wetted by contact with 94% by weight or less of MeOH aqueous solution; in some versions, the modified porous membrane may be contacted with 93% by weight or less of MeOH aqueous solution. Wet; in some versions the modified porous membrane may be wetted by contact with 92% by weight or less of MeOH aqueous solution; in some versions the modified porous membrane may be wetted by contact with 90% by weight or less of MeOH aqueous solution. In such embodiments, the unmodified porous membrane may be wetted by contact with a 97% by weight aqueous solution of MeOH. The APMW plasma treated membrane having improved wettability prepared by this method substantially retains the strength properties of the untreated membrane and is determined by contact with a liquid containing a gas (such as an autoclave in a membrane and water). Tested) is not dehumidified. The APMW plasma treated membrane having improved wettability prepared by this method substantially retains its contact wettability with a solution of methanol and water such that the concentration of MeOH in the solution is about 1% or less. Within the scope; the porous membranes retain their wettability for a period of time greater than about 10 days, and in some versions greater than about 70 days. In some versions of the invention, The APMW plasma treated film retains its contact wettability after storage in air at ambient conditions for 10 days or more (and after 70 days or more in some versions).

Atmospheric pressure microwave plasma treatment conditions may be selected to provide a surface modified porous membrane having a strength equivalent to at least 70% of the strength of the unmodified base porous membrane having no atmospheric pressure microwave plasma modified surface, at some These types are at least 80%, or at least 90% in other versions, and at least 95% in other versions. For example, the tensile strength of the film can be characterized and compared to an untreated porous film. The tensile strength of the sample can be measured in the machine direction (MD) and the web direction (WD) by taking a sample of the porous film (for example, about 2.5 cm × 7.5 cm). The ends of the film sample can be clamped (with a spacing of 2.5 cm between them) and then stretched from one end. The force data for the stretched film sample can be recorded and the maximum load when the film sample breaks can be determined. The tensile strength of the modified or control porous membrane sample can be calculated based on the measured maximum load and sample size.

The microwave frequencies that can be used to fabricate the modified film in the form of the present invention can include microwave frequencies above about 300 MHz. The microwave frequencies that can be used to treat the porous base film in certain versions of the invention can range from about 800 MHz to about 2450 MHz. In some versions of the invention the source has a microwave frequency of about 2.45 GHz (2450 MHz).

The method may further comprise or comprise combining the APMW plasma-modified membrane with one or more supports such as, but not limited to, webs, screens, filter cartridges, filter cages, end caps, or any combination thereof. The action of an exchange cartridge that can be used for mass and/or heat transfer operations is formed. The method can further comprise the act of pleating the APMW plasma modified film prior to bonding.

The APMW plasma treated porous membrane can be used to remove impurities, exchange energy, or any combination of these with fluids that contact the modified membrane. The conditioned fluid can be used in a chemical reaction or process with other liquids, powders or matrices.

Atmospheric pressure microwave plasma treatment of the porous membrane for a period of time that provides contact wettability, film strength, stable wettability, non-dehumidification, or a combination of such properties To be combined and to the extent. The porous membrane can be treated in a static (batch) mode, a continuous process, or a combination of the above. In some versions of the invention, the film is modified when in contact with the moving or rotating electrode of the plasma generating device. The plasma treatment can be carried out in a single plasma exposure, in a continuous exposure process on the web or film of the porous membrane, or it can include one or more passes through atmospheric pressure microwave plasma. In some versions of the continuous processing process, the rate at which the porous membrane passes through the microwave plasma can range from about 1 meter per second to about 25 meters per second. In some versions, slower processing speeds can be used to achieve better processing results. In some versions of the process, the film or its partially modified form may pass through the plasma in a range of from about 1 to about 10 times. In some versions the porous membrane is treated with an APM plasma for from about 30 seconds to about 180 seconds.

The plasma generation parameters used in the versions of the invention are not limited to any particular density or power unless they are selected to produce a porous membrane having properties such as, but not limited to, stable wettability, large base film Partial mechanical strength, low content extractables, non-dehumidified porous membranes or combinations of these. In some versions the porous membranes can be treated at a total power density in the range of from about 30 to about 150 watts/cm<³>. In some versions, the plasma treatment density can range from about 90 to about 510 watt-seconds/cm ² . The power can range from about 400 w to about 2400 w. In some versions the power can be 2400 watts or more. Optional pre- and post-plasma exposure treatments can be selected to further functionalize the membrane surface.

The present invention can include a porous membrane and a method of making the same, wherein the porous membranes have been treated with an APMW plasma in the presence of a gas initially present or fed to a plasma device, wherein the treatment is compared to an untreated porous membrane sample The contact wettability of the porous membrane is improved. For example, purification sources such as rare gases (such as helium or argon), reactive gases (such as oxygen), inert gases (such as nitrogen), inert gases or rare gases or more complex gaseous molecules (such as carbon dioxide and ammonia) The gas can be fed into or present in the plasma. In various embodiments, the gases can be used in a mixture (two or more gases). Examples of suitable mixtures may include, but are not limited to, air; with a controlled amount of additional vapor (such as water or other oxygenated liquid) Ultra-clean dry air source (see, for example, Parekh et al., International Publication No. WO 2005/010619, issued on July 21, 2004, Lithographic Projection Apparatus, Gas Purging Method, Device Manufacturing method and Purge Gas Supply System, The manner is fully incorporated herein; a rare gas or mixture of inert gases having an oxygen source other than air; a rare gas and an oxygen-containing gas, or other suitable gas mixture may be used. In some versions of the invention, the plasma is derived from a gas comprising an oxygen source. For example, an inert gas or a mixture of a rare gas and oxygen. In some versions the source of oxygen can be, but is not limited to, air, oxygen, carbon dioxide, water vapor, or a combination thereof. In some versions the source of oxygen can include vapors produced from oxygenates (such as peroxides), organic liquids (such as methanol), water, or combinations thereof. In some versions the source of oxygen is a gas such as ozone, ozone and oxygen, sulfur dioxide or a gas other than air. In some versions, a gaseous mixture comprising an oxygen source can be combined in relative proportions to form a different gas and oxygen mixture than the mixture found in air. In some versions of the invention, the film is modified using a plasma obtained from an air atmosphere. The rare gas system refers to He, Ne, Ar, mixtures of such and the like, wherein the rare gas system is present in an amount higher than that found in air.

The gas pressure that forms the atmospheric plasma maintains the plasma and interacts with the porous membrane to alter its properties. In some versions of the invention, the pressure of the plasma chamber can be maintained without the use of a mechanical vacuum pump. The pressure of the plasma can be approximately equal to atmospheric pressure. In some versions of the invention, the pressure of the chamber in which the membrane is treated using atmospheric pressure microwave plasma may be in the range of atmospheric pressure ± about 250 Torr, and in some versions the pressure may be at atmospheric pressure ± about 50 Within the scope of support. Pressures other than atmospheric pressure that can be achieved without the use of a mechanical vacuum pump can be used to vary the temperature, mean free path, and number of gases that interact with the surface of the porous membrane.

Membranes treated by atmospheric pressure microwave plasma can be used in filtration devices such as stacked disks (disc and frame modules), spiral wound modules, filter cartridges, filter cartridges, flat plates, hollow fiber modules. The APMW plasma treated membrane can be bonded to one or more supports, filter elements, Filter cage, or one or more end caps. These supports, filter elements, filter cages, some or all of the end caps or other fluid contacting surfaces may also be plasma treated. One or more screens or drainage layers may also be pleated and bonded to either side of the treated membrane. The membrane, the support, the filter element, the filter cage and the end cap treated by atmospheric pressure microwave plasma can be combined to form a filter cartridge. In some filtration applications, the filtration device may be in the form of a replaceable filter cartridge mounted in a housing or in the form of a permanently bonded cartridge having an input port and an output port in the process flow path. The filter cartridge can have a pleated membrane disposed in a cylindrical configuration.

The combination of atmospheric pressure, plasma gas, microwave frequency, and thermal conditions of the microwave plasma results in a film surface having chemical and physical structures that maintain its strength, provides stable contact wettability, and provides a non-dehumidifying film.

In the version of the invention, the surface of the porous membrane modified by atmospheric pressure microwave plasma has a chemical structure which provides higher wettability or higher surface energy than the unmodified porous membrane. The modification is stable such that the contact wettability remains substantially constant over time, or the wettability changes by 1% or less as the amount of MeOH in the solution for contacting the wetted film increases after the initial plasma treatment. In some versions of the treated film, after storage for at least 10 days in ambient air conditions (at least 30 days after some patterns, and after at least 70 days or more in some other patterns), wet Sex does not change over time. Stable contact wettability is beneficial because the treated film stored after plasma treatment has consistent properties during use or storage and is not subject to shelf life limitations.

Forming the treated substrate by the surface of one or more porous membranes modified by reaction or interaction with microwave plasma having a pressure drop in the range of about ±25% of the untreated membrane, sieve Partial particle retention characteristics, film strength, film thickness, or any combination of these; in some versions, within about ±15% of the untreated film, and in other versions about ±10 of the untreated film % or less. This is advantageous because existing membranes can be treated with APMW plasma without significantly adversely affecting their strength or physical structural properties.

The non-dehumidified surface of the atmospheric pressure microwave plasma modified membrane of the present invention may comprise polar functional groups formed on the surface of the porous membrane; the functional groups alter the chemical structure of the membrane surfaces. The functional groups can be formed by interaction or reaction of one or more gases in the plasma with the porous membrane. Such functional groups may include, but are not limited to, -COC-, -C-OH, -C=O, -C(F)=O; -SO ₃ H, -SO ₂ - and others which increase the wetness of the membrane surface A lyophilic and/or hydrophilic group of sexual or surface energy. By increasing the surface energy of the membrane surface, the membrane is more lyophilic and easier to wet with liquid contact. In some versions, where the liquid is water, contains water, or is an aqueous solution, the film can be characterized as being more hydrophilic. A more hydrophilic film is illustrated by the reduction in the amount of MeOH in the mixture with water that wets the film. A lyophilic surface is formed on one or more of the fluid contacting surfaces of the porous membrane by atmospheric pressure microwave plasma treatment.

In certain embodiments, surface polymer groups on one or more surfaces of the porous membrane are replaced by chemical groups during plasma processing, which may be referred to as activation. During activation, the plasma can break the polymer bonds on the surface of the polymer and replace or modify it with a carbonyl, carboxyl, hydroxyl or other desired group, such as an amine functional group. The activation is different from the deposition method in which a thin coating is formed on the surface of the film by chemical treatment or plasma treatment.

The surface of the modified membrane may have a composition whose surface has an oxygen/carbon ratio (O/C ratio) different from that of the untreated membrane by XPS analysis. In some versions of the APMW plasma modified film, the surfaces may have a composition having a surface having a fluorine/carbon ratio (F/C ratio) different from that of the untreated film by XPS analysis. In some versions of the invention, the O/C ratio can be between about 0.06 and about 0.08. In other versions of the invention, the O/C ratio can be between about 0.04 and about 0.08.

The porous membrane modified by atmospheric pressure microwave plasma has a surface structure and chemical properties that allow it to be contacted with a solution having a lower surface energy than the untreated membrane. For example, the surface energy of water can be altered by adding different amounts of readily miscible organic liquids, such as alcohols, to the water. In some embodiments, the porous polymer film treated by atmospheric plasma It has improved contact wettability, which can be determined using a variety of aqueous MeOH solutions. In some versions, the APMW plasma treated membrane having improved wettability can be wetted with a minimum amount of MeOH contact dissolved in an aqueous solution having a MeOH content comparable to that used to contact wet the porous membrane. The minimum amount of MeOH in the aqueous solution of the untreated sample is at least 1% by weight. In other versions, the minimum amount of MeOH in the solution contacting the wetted APMW plasma treated membrane sample is at least less than the minimum amount of MeOH in the aqueous solution used to contact the untreated sample of the porous membrane. 2% by weight (in some cases less than 3% by weight, and in other cases at least 4% by weight, and in other cases at least about 4% to about 7% by weight). For example, in some versions of the invention, the unmodified membrane may be wetted with 95 to 97% by weight aqueous MeOH solution, and the surface of the modified porous membrane prepared may be contacted with 96% by weight or less of MeOH aqueous solution. Wetting; in other versions the porous membrane has a surface structure and chemical properties that allow it to be wetted with the following solutions: 95% by weight or less of MeOH in water, 94% by weight or less in MeOH in water, 93% by weight or less in MeOH Aqueous solution, 92% by weight or less of MeOH in water or 90% by weight or less of MeOH in water. The lower the MeOH content in the solution, the higher the surface energy of the treated film, which improves the non-dehumidifying properties of the film. After storing as a dry film in the air at room temperature for at least 10 days in the surrounding environment (after storing in the surrounding environment for at least 30 days in some versions, and in other types for 70 days or more in the surrounding environment) Thereafter, the contact wettability of the film treated by atmospheric pressure microwave plasma is stable. This is beneficial for the long-term use of the filter and the consistent flow properties of the gas-generating liquid.

The porous membrane modified by atmospheric pressure microwave plasma has a surface structure and chemical properties that allow it to be contacted with a solution having a lower surface energy than the untreated membrane. For example, the surface energy of water can be altered by adding different amounts of readily miscible organic liquids, such as alcohols, to the water. The surface of the prepared modified porous membrane surface may be wetted by contact with 96% by weight or less of MeOH aqueous solution; in other versions, the APMW plasma treated porous membrane has a surface structure which allows the following solution to be contacted with the wetted surface structure and Chemical properties: 95 weight % or less of MeOH aqueous solution, 94% by weight or less of MeOH aqueous solution, 93% by weight or less of MeOH aqueous solution, 92% by weight or less of MeOH aqueous solution or 90% by weight or less of MeOH aqueous solution. The lower the MeOH content in the solution, the higher the surface energy of the treated film, which improves the non-dehumidifying properties of the film. Membrane treated by atmospheric pressure microwave plasma after storage in the ambient environment for at least 10 days (after at least 30 days in some versions and after 70 days or more in ambient air in other versions) The contact wettability is stable. This is beneficial for the long-term use of the filter and the consistent fluid properties of the gas-generating liquid.

The porous membrane treated by atmospheric pressure microwave plasma can be characterized by a nominal pore size that is directly related to the particulate retention characteristics of the membrane. In some versions the porous membrane is a sieving filter that removes particulates by a screening mechanism. The pore size is proportional to the size of the particles retained by the screening filtration and the pore size can be related to the flow rate through the membrane. It is desirable to simultaneously maximize particle retention and flow rate. It is not desirable to significantly increase one of these features while significantly reducing the other of these features, and can be avoided in the form of the invention, which does not use a solution based coating to modify the film. quality.

Atmospheric pressure microwave plasma treatment of the porous membrane can be used, for example, in terms of power density, processing time, number of treatments, feed rate of the membrane via plasma, or any combination of such, for processing during pure water filtration. The porous membrane substrate is generally not weakened, or exhibits a substantial increase in particle shedding, or exhibits substantial changes in particle retention, or exhibits substantial changes in pressure drop, or any combination of such film properties. Pure water can be deionized or distilled water. In some cases, the pure water may have a resistivity ranging from 2 ppb to 6 ppb or less, a resistivity of 17.7 million ohm-cm to 18.2 million ohm-cm or more, and for 0.05 micron. Water of an average particle count of less than 800 cells per liter in size. For example, the APMW plasma modified porous membrane of the present invention has substantially the same permeability (determined by pressure drop) as the unmodified porous membrane substrate. That is, the pressure drop of the modified porous membrane of the present invention is not changed in comparison with the pressure drop across the unmodified porous membrane substrate. More than ±25%. In some versions of the APMW plasma treated porous membrane, the pressure drop does not vary by more than ±15% compared to the pressure drop across the unmodified porous membrane substrate, and in some versions the change does not More than ±10%.

Films modified in accordance with the present invention may have particulate retention properties of the unmodified membrane while substantially maintaining the flux characteristics of the unmodified substrate. Additionally, the atmospheric membrane plasma treated porous membrane composition does not promote gas nucleation on the membrane surface upon contact with the degassed liquid or during filtration of the degassed liquid; the membranes can be characterized as being non-wetting. Thus, when filtering a degassed liquid such as, but not limited to, an SC1 or SC2 dedusting bath for wafers fabricated by microelectronics, the useful life of the film of the present invention is significantly greater than the useful life of the unmodified porous film. The porous membranes can be autoclaved and can be wetted by the liquid at all times.

A comparison of the SEM of the starting film with the APMW plasma treated film did not show a significant change in appearance. We anticipate that the sieving particle retention properties of the membrane do not change, or vary by about ±25% or less, ±15% or less of the sieving particle retention of the untreated membrane, and ±10% or less in some versions. Within the scope below. Based on this analysis, it is expected that the particle shedding of the treated film will be similar to the base film. The atmospheric pressure microwave plasma modified porous membrane of the type of the invention may be a microporous membrane having at least 3 sieved LRV for particles of 0.1 micron or less in the liquid; The particles of 0.05 microns or less may have a sieved LRV of at least 3; for particles of 0.03 microns or less in the liquid, there may be a sieved LRV of at least 3. The LRV or log reduction value means the log ₁₀ value of the number of particles in the feed (filtrate) divided by the number of particles in the permeate after passing through the membrane.

The surface of the porous membrane treated by atmospheric pressure microwave plasma may be free of ion extractables and/or organic extractables, and the extracts may be present in a coating material solution applied to the porous membrane to make it hydrophilic. . This minimizes extractables, such as trace amounts of ionic and organic materials that can contaminate the filtered fluid. In certain embodiments, the APMW plasma modified film has a total of less than about 200 ppb of extractable ions (such as sodium ions, calcium ions, zinc ions, iron ions, copper ions, potassium ions, and aluminum ions). In some embodiments, The APMW plasma modified membrane has a total of less than about 20 ppb of extractable ions (such as sodium ions, calcium ions, zinc ions, iron ions, copper ions, potassium ions, and aluminum ions). The extractables content of the modified porous membrane can be determined by immersing a portion of the membrane in a solution of HCl or nitric acid for one or more days and analyzing the acid solution by ICPMS or other suitable technique. The extraction solution can be 10% by volume of 37% HCl in deionized water. In some versions, the APMW plasma modified film has a TOC of less than about 20 ppb.

The porous membrane modified by the APMW plasma treatment may include a coating-free cast film, an extruded film, a coextruded film or a laminate film for filtering the liquid. The porous membrane may comprise a thermoplastic such as a halogenated polyolefin (e.g., polytetrafluoroethylene, modified polytetrafluoroethylene, perfluoro(vinyl alkyl ether), FEP), UPE, polyfluorene or other membrane material. A single porous layer, a layer or layers having a pore size gradient (eg, an extruded film or laminate film with one or more layers having different pore sizes). The porous membrane can comprise a variety of morphologies such as ribbons, strands and nodes, open honeycomb, nodular or other membrane morphology. The film can have a symmetrical or asymmetric pore structure. The thermoplastics used in the film in certain versions have a crystallinity greater than about 65%, in some versions greater than about 75%, and in other versions greater than about 85%. Without wishing to be bound by theory, the higher the crystallinity of the film, the more durable the lyophilic surface modification.

The porous membrane treated by atmospheric pressure microwave plasma may comprise one or more layers. In some versions, the porous membrane may include a filter layer supported by one or more support layers or layers of different porosity. The layers can provide support to the inner filter layer, such as a large aperture support layer on either side of the dense smaller pore filter layer. The layer can be a skinned membrane, can be a membrane with no discernible layer structure, or it can include a pore gradient or pore size distribution. The layers can be coextruded, laminated, bonded or melt bonded together. In some versions the porous membrane is a microporous membrane.

The membrane treated by atmospheric pressure microwave plasma of the present invention is integrated and has no pinhole defects. It can be used as a slab medium that retains sufficient strength for pleating and can be used to form a pinhole-free pleated film combination, or it retains sufficient strength for bonding to other supports. Example In other words, the APMW plasma treated film has sufficient strength and integrity to be pleated with one or more supports or drainage support mesh. The pleated APMW plasma modified film, drainage net, filter element, filter cage and end cap can be combined to form a filter cartridge.

In some versions of the invention, the porous base film has no externally coated monomer coating prior to atmospheric pressure microwave plasma treatment. Or in some embodiments, the gas used to form the plasma is free of polymerizable monomers.

The porous membrane substrate is a thin polymeric composition that can be used to separate impurities (such as particulates, ions, proteins, gels) from fluids or slurries. In some versions the porous membrane has retention and structural features of the sieving filter because it removes particulates by a screening mechanism, as opposed to deep media. The membranes may be ultrafiltration or microfiltration membranes which, after treatment with APMW plasma, become contact wettable with aqueous MeOH solution, wherein the minimum amount of MeOH in the aqueous solution used to contact the wetted porous membrane is less than The minimum amount of MeOH in the control aqueous solution that contacted the untreated sample of the porous membrane was contacted. In some versions the porous membrane is a microporous membrane or an ultrafiltration membrane. The membrane pore size can range from about 10 microns to about 0.001 microns. The film substrate can have any convenient geometric configuration that can be subjected to atmospheric pressure microwave plasma treatment to form a lyophilic or hydrophobic surface on portions of the film, including flat sheets, corrugated sheets, hollow fibers, or the like. The film may be supported or unsupported and may be isotropic or anisotropic, skinned or unskinned or may be a composite film. The film substrate can have a thickness of between about 5 microns and about 250 microns, preferably between about 10 microns and about 200 microns, and more preferably between about 10 and about 30 microns. The porous membrane substrate may comprise a porous or microporous halogenated polyolefin such as polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, and the like. The porous membrane substrate may comprise a polyolefin such as polyethylene (which includes ultrahigh molecular polyethylene (UHMWPE) having a molecular weight of between about 1 million and about 6 million), polypropylene, and polymethylpentene. The porous membrane may include polyfluorene, polyether oxime, polyimine, and polyamine. The fluoropolymer may include polytetrafluoroethylene (PTFE), fluorinated ethylene-propylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer or perfluoroalkoxy polymer (PFA). In some versions the fluoropolymer may be at least 98% tetrafluoroethylene, having A modified PTFE resin of a modifying agent such as, but not limited to, hexafluoropropylene, perfluoro(alkyl vinyl ether), the like, or other mixtures. In some versions of the invention, the porous polymer is PTFE or expanded PTFE.

In one version of the invention, a surface modified porous membrane having an average pore diameter of 0.05 microns or less is formed. The film is formed from a fluoropolymer film substrate comprising polytetrafluoroethylene. The surface of the porous membrane substrate was modified by a microwave plasma apparatus having an atmospheric pressure of greater than about 400 watts. The plasma-modified porous membrane may be wetted by contact with a MeOH aqueous solution containing 96% by weight or less, and the modified porous membrane is non-dehumidified, and the membrane is autoclaved in water at a temperature of about 135 ° C for about 40 minutes. Keep it translucent afterwards.

Atmospheric pressure microwave plasma treatment changes the surface energy of one or more of the plasma treated porous membrane surfaces. The surfaces can include an outer operating surface as well as an inner pore surface. One of the one or more fluid contacting surfaces of the polymeric porous membrane may be treated with an APM plasma, or all of the fluid contacting surfaces of the porous membrane may be completely modified by atmospheric pressure microwave plasma. Both sides of the porous membrane can be treated in the plasma using one or more passes through the processing chamber. The higher the surface group density formed on the surface of the porous film, the higher the wettability and the higher the resistance of the porous film to dehumidification when filtering a gas-containing liquid, a gas generating liquid or the like.

The pressure drop across the filter is a measure of the resistance of the filter to liquid flow. High pressure drop indicates high liquid flow resistance, such as when the filter is dehumidified or clogged with gas or particulates in the pores of the membrane. Low pressure drop represents low liquid flow resistance, such as when the filter is new and completely wet. In most cases, the pressure drop data should be considered relative to the same filter before and after atmospheric microwave plasma treatment. The pressure differential across the filter can be measured as a pressure drop in pounds per square inch (psi) or Pascal, at a constant liquid flow rate of 1.0 US gallons per minute (gpm) or 3.78 liters per minute (lpm). During the test, pure water was preferably used on the pre-wetted and rinsed filter to measure the pressure drop.

Contact wettability refers to a test liquid sample applied to a portion of a porous membrane throughout The ability of the film thickness to fill the pores of the film. The wetted portion of the film appears to be transparent compared to the unwetted portion of the film. Contact wettability refers to the ability of a test liquid sample applied to a portion of a porous membrane to fill immediately across the thickness of the membrane or to fill the pores of the membrane in about 1 to 2 seconds, such that the membrane portion is wetted relative to the uncoated liquid. The opaque appearance of the film is shown as transparent. The wetted portion of the porous membrane allows liquid to flow through the membrane. Conversely, the base film or the porous membrane treated by APMW plasma to render it lyophilic or hydrophilic but undertreated will remain opaque when the test liquid is applied, or the coated liquid portion of the film may be slow ( Wetting begins at greater than about 5 to about 15 seconds.

The wetting properties of the film can be determined by applying a test liquid having various surface energies to the plasma-modified polymer film of the present invention.

The surface of the contact-wettable polymer porous membrane modified by atmospheric pressure microwave plasma is also non-dehumidified. Non-dehumidification means that the modified porous membrane composition is still wetted by the liquid after contacting or filtering the liquid containing the gas; the gas does not discharge enough liquid from the pores of the membrane to increase the surface of the membrane treated by the APMW plasma. Opacity, pressure drop or flow time characteristics. Any increase in more than 25% of these properties is considered a dehumidification film.

The non-dehumidifying properties of the APMW plasma treated porous membrane of the present invention can be determined by heating a liquid wetted membrane sample in an autoclave having a temperature above the boiling point of the liquid. If the porous membrane sample is not dehumidified, the sample will remain wet and translucent after autoclaving. For example, if the wet porous membrane sample treated with the APMW plasma is non-dehumidified, the sample will remain wet and translucent after autoclaving. If the wet base film or the wet porous membrane treated by APMW plasma to make it lyophilic or hydrophilic but undertreated is subjected to the same autoclave treatment, it will be dehumidified after autoclaving and appear to be opaque. In another illustrative example, the APMW plasma treated PTFE porous membrane wetted with water is non-dehumidified if it remains translucent after autoclaving at 135 ° C for 40 minutes in water. Non-dehumidification is different from the measurement of the contact angle of the surface energy of the film, since non-dehumidification refers to the wetting property of the film across the thickness of the film and not only to the outer surface of the film.

Dewetting can be measured on the treated porous membrane sections. The film can be wetted with a liquid having a low surface tension. For example it can be wetted with isopropyl alcohol followed by rinsing or rinsing with water to remove the IPA from the film. The film can be placed in a vessel with water and placed in an autoclave at 135 ° C for about 40 minutes. During the autoclave process, the gas dissolved in the water will escape from the solution, the solubility of the gas in the autoclave in the water is reduced, and the gas can displace the water in the untreated membrane. This is an example of a gas-containing liquid in contact with a membrane. The flow time before and after the autoclave treatment can be performed to measure the change in flow time after the autoclave treatment. An increase in deionized water flow time of more than 25% after autoclaving can be used to characterize the dehumidified membrane.

The APMW plasma modified porous membrane composition also prevents or reduces the dewetting of the membrane during exposure to a gas, such as air, as long as the membrane is not exposed for a time sufficient to cause the membrane to dry. This can be determined, for example, by a change in the weight of the wet film sample compared to its weight upon drying. During use in the filtration process, the filter can be exposed to air at a small differential pressure across the filter, such as during replacement of the filtered liquid.

The flow time of the porous membrane sample can be determined by wetting the membrane sample with a low surface tension liquid and then rinsing the membrane to remove residual wetting liquid. Where the pressure into the membrane is fixed and the volume of liquid is known, the time it takes for the liquid to flow through one of the regions of the membrane (which can be temperature corrected for viscosity) can be determined. For dense membranes, the flow time is longer than for opener membranes. For example, a pressure of about 10 to 12 psi can be used to flow about 100 ml of water through a porous membrane having an area of about 20 cm ² wetted with IPA and rinsed with water, and the time measured. The test can be performed on a control sample of the porous membrane, on the APMW plasma treated sample, and on the autoclaved sample, and the flow time and temperature are measured. This test can use filtered water as the liquid. It helps to rule out other potential flow rate reduction effects due to differences in viscosity in the liquid or due to increased flow resistance caused by particles removed from the liquid which may be trapped on the membrane surface.

Forms of the invention can include an APMW plasma treated membrane configured to remove contaminants from a liquid in a fluid flow circuit. The membrane can be configured in a filter cartridge and used in recycling or single In the wafer cleaning device, the filter is removed from the SC1 or SC2 dust removal bath.

The blister point pressure test can also be used to characterize the degree of dewetting observed in the APMW plasma treated porous membrane or control porous membrane. In general, the lower the bubble point pressure of the membrane, the higher the potential for dewetting when exposed to air. The blister point pressure of the APMW plasma treated porous membrane of the present invention is greater than the blister point pressure of the modified porous membrane substrate or the control porous membrane substrate. The bubble point pressure test method measures the pressure used to force air through the pores of the membrane previously filled with water.

APMW can be measured as determined by the modified SEMATECH particle retention method described in Millipore Corporation Technical Document MA041 (available from Millipore Corporation, Bedford, Mass., USA, and incorporated herein by reference) The microparticle retention properties of the plasma treated porous membrane were compared to a porous membrane having an unmodified surface. In some versions of the invention, it is contemplated that the particle retention properties of the treated film are substantially the same as those of the unmodified film (differences are in the range of about ±25% or less).

Example 1

Atmospheric pressure microwave plasma treatment of a multilayer (support layer, filter layer, support layer) 0.03 micron PTFE membrane sample was performed using different gas species, flow rates, power, voltage, and processing time (linear velocity). In this example, the film was cut into 12" x 4" pieces and subjected to atmospheric plasma treatment on a rotating electrode (one electrode was moving and the other electrode was fixed) under various conditions. The experimental conditions and results are listed in Table 1.

The strength (maximum loading) of the control porous membrane and the APMW plasma-modified porous membrane is summarized in Table 1. The results show that the modified membrane retains more than 70% of its original strength (substantially) and has improved wettability compared to the control sample. Through the selection of the conditions, the strength of the modified membrane may be 80% or more, 90% or more and 95% or more of the untreated porous membrane. Higher strength is advantageous because it allows for higher pressure differentials and/or temperatures while maintaining film integrity; it also provides higher yields during bonding and cartridge manufacturing operations.

The initial treatment of porous membranes (samples 1 to 12) treated with atmospheric plasma is also provided in Table 1. Contact wettability after (day 0) and after long-term environmental storage (day 71). The contact wettability of each porous membrane after APMW plasma treatment was improved relative to the control sample because less MeOH (by weight) of the test liquid could be used to contact wet the APMW plasma treated porous membrane. The wettability after long-term storage in air showed no change in contact wettability after 71 days, except for the samples produced under the conditions of sample 9. In Sample 9, the wettability of the contact was slightly changed, and the amount of MeOH used to wet the film was increased from 93% by weight to 94% by weight. The film has better wetting properties compared to the control sample. These results demonstrate that APMW plasma treatment of porous membranes can be used to form stable, contact-wettable porous membranes.

The results of the samples of Examples 2 to 12 in Table 1 show that the wettability is improved after atmospheric plasma treatment. These results show that a polymer porous membrane treated by atmospheric pressure microwave plasma in the presence of a gas such as a mixture of He or He and an oxygen source can result in contact with the wetted modified porous membrane with an aqueous MeOH solution, wherein The minimum amount of MeOH in the aqueous solution contacted to wet the porous membrane is at least 1% by weight less than the minimum amount of MeOH in the control aqueous solution used to contact the untreated sample that wets the porous membrane, and in some Less in the situation At least 2% by weight. The surface tension (in dynes/cm) of various aqueous methanol solutions can be found in Lange's Handbook of Chemistry, 11th edition. For example, untreated sample 1 (initial 0.03 μm PTFE membrane) may be wetted with an aqueous MeOH solution having a concentration of MeOH equal to or greater than 95% by weight. After atmospheric pressure microwave plasma treatment, the modified membrane may be wetted with 93 to 94% by weight of MeOH solution, which indicates better wettability and lower surface energy of the modified membrane. The results also show that after initial wetting and air drying, the film is stored for 10 days or more in ambient air at room temperature and retains its contact wettability after 70 days or more. These results indicate that the APMW plasma modification system is stable such that the contact wettability remains substantially constant over time, or may be wet after the initial plasma treatment by adding MeOH to the aqueous solution used to contact the wetted membrane. The sex change is 1% or less (see, for example, example (9)).

Example 2

Table 2 lists the conditions and results of atmospheric pressure microwave plasma treatment of a single layer 0.05 micron PTFE porous membrane.

Sample 13 shows that the wettability is improved after atmospheric plasma treatment and the film retains more than 80% of its strength. The untreated control sample (initial 0.05 micron PTFE membrane) may be wetted with a MeOH solution having a MeOH concentration equal to or greater than 97% by weight. After atmospheric pressure microwave plasma treatment, the modified membrane sample 13 can be wetted by contact with a 96% by weight MeOH solution, which indicates better wettability. These results show that the film retains its contact wettability after storage for 10 days or more under ambient conditions and after 70 days or more. For example, the wetted APMW membrane is initially contacted with a plurality of aqueous MeOH solutions to determine the contact wettability of the sample. Sex, and then the modified membrane is allowed to dry in air. After storage for 10 days at room temperature (ambient conditions) in air, the wet-dried modified film was contacted with an aqueous MeOH solution to measure the contact wettability of the modified film again. The wet film was allowed to dry, and after a total of 71 days of storage under ambient conditions, the wet dried modified film was contacted with an aqueous MeOH solution to again determine the contact wettability of the modified film.

Example 3

The untreated 0.05 micron PTFE porous membrane and the 0.05 micron PTFE porous membrane treated with atmospheric pressure microwave plasma were first wetted with isopropyl alcohol, followed by complete rinsing or rinsing with water. The porous membrane sample was placed in a disc holder under restraint and immersed in distilled water in an autoclave at 135 ° C for 40 minutes. The deionized (DI) water flow rate on the autoclaved samples (control membrane and APMW plasma treated membrane) was measured at a positive pressure of 14.2 psi before and after autoclaving. The results are shown in Table 3.

APMW: treated by atmospheric pressure microwave plasma.

For the unmodified membrane, "APMW front", Table 3 shows that the autoclave treatment resulted in a flux loss of about 11 to 33% caused by membrane dewetting. However, as shown in Table 3, the APMW plasma modified membrane samples were non-dehumidified and did not exhibit any flux loss after one autoclave test cycle.

Table 3 shows that the flow time of the membrane treated by atmospheric pressure microwave plasma was not reduced relative to the membrane before APMW treatment. Without wishing to be bound by theory, this flow result may imply that the membrane pores expand due to the stretching of the membrane on the non-optimized tensioner.

Example 4

Prepare a vacuum plasma treatment of a multilayer (support layer, filter layer, support layer) 0.03 micron PTFE membrane sample in helium (Table 4) and hydrogen (Table 5) to provide contact in a 94% by weight aqueous MeOH solution. Wetability of the modified membrane. The vacuum plasma treated films have a slightly lower or substantially the same contact wettability as compared to those of Table 1 (compared to Sample 1). The strength test results show that the vacuum-treated sample can be obtained at almost the same power (250 to 300 watts) compared to the power used in the APMW plasma-treated sample (400 to 2400 watts). Reduce the modified porous membrane by half. It has also been observed that under these conditions, the vacuum plasma treatment time for the porous membranes for about 1 minute does not form a modified PTFE porous membrane that can be wetted with 94% MeOH (use a shorter time to try to minimize Film strength degradation under vacuum plasma conditions - the results of this short treatment are not given in Table 4 or Table 5).

Flow time tests were performed and these tests indicated that the flow time was not reduced by vacuum plasma treatment. The flow time test was performed at 14.2 psi using a UPE disc holder.

These comparative results show the use of APMW for the same grade of wettability The slurry treatment can form a film that is stronger than the vacuum treated film. Higher strength porous membranes are advantageous for bonding and/or pleating the modified membrane to the device, and because higher strength membranes can withstand higher process pressures and temperatures without loss of integrity, it is advantageous .

Example 5

This example illustrates atmospheric pressure microwave plasma treatment of porous membranes and their contact wettability and strength. For this experimental setup, the membrane was treated 10 times in the plasma using a power of 2.4 KW and a helium flow rate of 3 slm or a still air environment. In this example, the sample has a film thickness of from about 15 to 20 microns, and typically less than about 30 microns.

The strength of the film was measured in the web direction (WD) and the machine direction (MD). The intensity of the control samples (14, 23 and 32) is given in Table 6, and it is about 24 Newtons (N) or more. The treated sample (eg, 34) has a WD of 12.7 N and a MD of 22.7 N, which averages about 70% of the control sample. In another sample (eg, sample 18), the intensity was WD of 32.8 N and the MD of 40.7 N, which averaged about 73% of the control sample.

The results of these experiments are summarized in Table 6, and it is shown that a modified film having improved contact wettability and an average strength of about 70% or more of the starting porous film can be produced. The O/C ratio of the microwave modified membrane at atmospheric pressure is different from that of the untreated membrane. The ratio is in the range of from about 0.04 to about 0.08 in the samples. Sample 18 has an O/C ratio of 0.063; sample 19 has an O/C ratio of 0.064; sample 34 has an O/C ratio of 0.077; and sample 39 has an O/C ratio of 0.044.

These results show that a polymer porous membrane treated with atmospheric pressure microwave plasma in the presence of a gas (including a gas such as He or air) results in a wetted porous membrane that can be wetted with an aqueous MeOH solution, wherein the contact is wetted. The minimum amount of MeOH in the aqueous solution of the porous membrane is at least 1% by weight less than the minimum amount of MeOH in the control aqueous solution used to contact the untreated sample that wets the porous membrane, and in some cases at least 2 weight less %, in other cases at least 3% by weight, in other cases at least 4% by weight, and in some In the case of at least about 4 to about 7% by weight. For example, untreated sample 14 (initial 0.03 μm PTFE membrane) may be wetted with an aqueous MeOH solution having a MeOH concentration equal to or greater than 97% by weight. After atmospheric pressure microwave plasma treatment in an atmosphere with helium gas flow, the modified membrane can be wetted by 94% by weight (sample 16 to 18) MeOH solution, which is a 3% reduction in MeOH concentration and indicates better. Wet. The untreated sample 32 (initial 0.05 μm PTFE membrane) may be wetted with an aqueous MeOH solution having a MeOH concentration equal to or greater than 97% by weight. After atmospheric pressure microwave plasma treatment in an atmosphere with an air flow, the modified membrane may be wetted by 90 to 93% by weight of a MeOH solution (samples 37 to 40), which has a reduced MeOH concentration of 4 to 7% by weight and Indicates better wettability.

Although the invention has been described in considerable detail with reference to certain preferred preferred embodiments of the invention, other variations are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description contained in the specification and the preferred variations.

Claims (10)

A composition comprising a multilayer halogenated polyolefin microporous membrane comprising: a filter layer, and a support layer, the microporous membrane being non-wetting and being contactable with an aqueous solution of 94% by weight or less of methanol Wetting, having a strength of at least 20 Newtons and a thickness of less than about 30 microns, comprising one or more surfaces having an O/C ratio greater than about 0.06, and having at least 0.1 micron or less of particles in water 3 LRV. The composition of claim 1 wherein the halogenated polyolefin is polytetrafluoroethylene or modified polytetrafluoroethylene. The composition of claim 1, wherein the microporous membrane is wetted by contact with 96% by weight or less of an aqueous MeOH solution, and subjected to autoclaving in water at a temperature of about 135 ° C for about 40 minutes to be non-dehumidified. of. The composition of claim 1 wherein the filter layer and the support layer are coextruded, laminated, bonded or melt bonded together. The composition of claim 1, wherein the filter layer and the support layer are pleated together. The composition of claim 1 wherein the microporous membrane has an O/C ratio of from about 0.06 to about 0.08. A filter comprising the composition of claim 1. The filter of claim 7, wherein the composition comprises a multilayered halogenated polyolefin microporous membrane having a total of extractable ions of less than about 200 ppb, including calcium ions and sodium ions. A method of making the composition of claim 1, the method comprising the steps of: contacting the filter layer with atmospheric pressure microwave (APMW) plasma, the APMW electricity Slurry treating one or more layers of the filter layer to improve contact wettability of one or more of the filter layers; and bonding or pleating the APMW plasma modified filter layer to a support layer. The method of claim 9, wherein the APMW plasma modified filter layer is pleated prior to bonding with the support layer.